30th April 2024

A 7-year-old girl presents with a history of recurrent painful swelling of the hands and feet, and a recent episode of severe abdominal pain.

A 7-year-old girl presents with a history of recurrent painful swelling of the hands and feet, and a recent episode of severe abdominal pain. Her parents mention she had jaundice as a newborn. She has no significant past medical history or family history of similar symptoms.

Investigations:

Haemoglobin: 95 g/L (115–155)

MCV: 75 fL (76–96)

White cell count: 12.4 × 10^9/L (4.5–13.0)

Platelets: 305 × 10^9/L (150–450)

Reticulocyte count: Elevated

Which initial investigation is most likely to help establish a diagnosis?